To permit long-term preservation of food products, various different methods, such as canning or sterilization, pasteurization, deep-freezing, ionization by irradiation, and lyophilization, are well known at present.
Sterilization is a preservation method that in its conventional form breaks down the processed food products on the organoleptic level and in particular affects their taste and appearance. Because of this, it does not enable the manufacture or preparation of top-quality products. Consequently, the method is not used on a large scale except for processing food products that are not initially top quality products.
Deep-freezing is a preservation method that also causes irreversible physical-chemical degradation in the processed products, particularly affecting the proteins and starch that they contain, because the processed products are exposed to below-zero cold. For this reason, this method is again not used except to prepare products that are not of top quality.
Refrigeration is a satisfactory preservation method from the organoleptic standpoint, even though the storage life of refrigerated food products is quite short. However, this method has the disadvantage of not disrupting microbial or enzymatic activity. In particular, the spores of Clostridium botulinum type E, which among microorganisms present in food products are the most dangerous for the human organism, can germinate under certain temperature conditions which are encountered in preservation at above-zero cold, in particular as soon as the the temperature rises above 2.2.degree. C.; and beginning at +3.degree. C., the germinated spores can grow.
Lyophilization is a preservation method which is quite tedious to use, and moreover it is again reserved for food products or primary materials that are not of high quality.
Preservation of fresh food products at above-zero cold and in a vacuum is a method that does slow down or stop the development of the majority of aerobic microbial flora. In certain cases, however (elevated pH, elevated microbial burden, insufficient lactic flora), it can promote the germination and growth of the most dangerous microorganisms (Clostridium botulinum) and additionally can permit the formation of zones, in the form of exudates and substrates, that are particularly favorable to the development of all bacteria, whether strictly or only selectively anaerobic.
Finally, ionizing irradiation is authorized only for certain products, at irradiation doses such that they reduce but do not completely destroy the microbial burden. Moreover, sterilizing doses, which degrade the food products, are dangerous to public health and are authorized only for the packages themselves. Another disadvantage of this preservation method is that the irradiation apparatus is extremely expensive. Known preservation methods hence have the common disadvantage that none of them allows the simultaneous assurance of complete microbiological safety, respecting the initial organoleptic, nutritional and rheological quality and characteristics of the processed food products, while being usable for a very wide range of food products, and finally being usable without major capital investment.